I have 6 list of Objects in Java with a data structure like this:

Class MyObj {
    int identifier;
    Class someOtherClass;
}

Every List in the 6 Lists is a List<MyObj>.

I want to build a final list which does merge sort while reading all the 6 lists and prepare a final list.

I believe Merge Sort or similar solution is the way to go. I looked at comparator example as well but could not find one matching my requirements. Can someone suggest a library or existing API that can help me accomplish this task?

I also found a solution at How to Sort a List<T> by a property in the object but it does inArray sort, it does not tke account of multiple Lists.

All 6 Lists are already Sorted, I need combined sorted List